A foamable composition is formed by mixing an isocyanate compound with a hydroxyl-containing material, such as a polyol (i.e., a compound that contains multiple hydroxyl groups), typically in the presence of water and a catalyst. The isocyanate and polyol precursors react to form polyurethane. At the same time, the water reacts with the isocyanate compound to produce carbon dioxide. The carbon dioxide causes the polyurethane to expand into a foamed cellular structure (i.e., a polyurethane foam), which may be used to protect or cushion a packaged object.
In “foam-in-bag” packaging, a machine produces flexible containers (e.g., bags) from flexible, plastic film, and dispenses a foamable composition into the containers as they are being formed. As the composition expands into a foam within the container, the container is sealed shut and typically dropped into a carton (e.g., a box), which holds the object to be cushioned. The rising foam expands into the available space within the carton, but does so inside the container. Because the bags are formed of flexible plastic, they form individual custom foam cushions around the packaged objects. Exemplary types of such packaging apparatus are described, for example, in U.S. Pat. Nos. 4,800,708; 4,854,109; 5,027,583; 5,335,483; 5,376,219; 6,003,288; 6,472,638; 6,675,557; 7,607,911; and 8,869,859, each of which is incorporated herein in its entirety by this reference; and in U.S. Pat. App. Pub. 2007-0252297 A1, which is incorporated herein in its entirety by this reference.
In “foam-in-place” packaging, the cushioning foam is generated while an article to be protected is being packaged. For example, when polyurethane foam precursors are mixed to react and generate the polyurethane foam, by the time that the urethane foam forms and hardens (i.e., “sets”) the resulting foam has expanded to fill the void spaces in the closed container and thereby cushion the object being packaged. As the composition foams to fill the remainder of the closed container, it forms a custom-shaped foam cushion surrounding the object. The object to be packaged may be covered with a polymer film or other material to protect the object from the liquid foamable composition (i.e., a mixture of the reactant precursors) that is injected or dispensed into the container onto the polymer film.
In either system, a dispenser receives, and may initiate mixing of, the foam reactant precursors from (typically) two separate supply containers (e.g., supply drums), then dispenses or injects the reactive mixture. Examples of such dispensers are described, for example, in U.S. Pat. Nos. 3,687,370; 3,945,569; 4,023,733; 4,159,079; 4,426,023; 5,186,905; 5,255,847; 5,791,522; 5,950,875; 6,811,059; 6,929,193; and 6,996,956, each of which is incorporated herein in its entirety by reference. Such systems may operate periodically or on-demand as an operator actuates the dispenser, thereby periodically activating the pumps to supply the foam precursor liquids.
Some systems for making foam-in-bag or foam-in-place polyurethane foam use a pump that is submerged within the precursor reactant liquid in the supply container. This is advantageous in that the pump located at or near the bottom of the container takes advantage of the pressure generated by the column of liquid in the container to assure sufficient suction pressure head to the pump. Further, since some types of precursor reactant liquids, such as isocyanates, will react with moisture in the air to form a hard crystalline structure or residue, the submersion of the pump in the container will minimize the chance that liquid leakage from the pump will react with ambient moisture.
However, the arrangement of submerging the pump in the supply container may necessitate a difficult and perhaps messy changeover process to withdraw the pump from an empty supply container and install it in a full supply container.